Abstract

Sedimentological studies of six Holocene lakes in the Coorong region of South Australia have revealed the presence of a calcrete layer at a similar stratigraphic level in all of these lakes. The calcrete layer lies at <1.5 m subsurface depths within each of the lakes and is exposed along the marginal areas of some. Mud-crack polygon and desiccation cracks are well preserved in exposed parts of the calcrete surface, and the calcrete exhibits vadose-zone diagenetic fabrics. These features provide direct evidence for the existence of a late Holocene major Australian arid period during which the lakes in the Coorong region remained dry and the surfaces of lake sediments underwent calcretization. Radiocarbon dating of the calcrete layer indicates that this period existed from 3300 to 1300 yr B.P.